It's personal!

Although it was originally pitched to adults, teens co-opted the transistor radio. In the late 1950s, prices fell, rock and roll took off, and AM radio stations began to spin Top 40 hits. Teens tuned in and sales of the handheld units, many imported from Japan, soared. Portability and a single plug-in earphone made listening a personal experience—one teens did not have to share with their hopelessly square parents.